Retractable cover for swimming pools



Jan. 22, 1963 B. lsAAcsoN RETRACTABLE COVER FOR SWIMMING PooLs Original Filed May 6, 1958 3 Sheets-Sheet 1 i llM, -..l1

INVENTOR. .Boe/.s lswcso/v lIan. 22, 1963 B. xsAAcsoN RETRACTABLE COVER FOR SWIMMING POOLS Original Filed May 6, 1958 3 Sheets-Sheet 3 G .104

INVENTOR.

,Boe/.s lsnncso/v rroeA/Eys.

States This invention relates to covers for swimming pools or the like and intended primarily as a safety feature to prevent persons, especially children, from accidents in connection with hazardous bodies of-water. The apparatus is also intended to assist in maintaining the pool or body of water clean.

Prior swimming pool covers have required tedious operations to secure them in position. Thus, for example, a series of stakes have been provided along and about the periphery of the pool for tying the edges of the cover in position. Operations such as this are quite cumbersome and lead ultimately to laXity so far as covering the swimming pool is concerned. Many prior swimming pool cover structures have required tracks, brackets, and other equipment located entirely about the periphery of the pool. This of itself creates a hazard during the normal use of the pool. The primary object of this invention is to provide a simple swimming pool cover structure which substantially eliminates these disadvantages.

Another object of this invention is to provide a device of this character that provides not only a cover for a swimming pool. but also a cover for the operating mechanism of the cover.

Another object of this invention is to provide a swimming pool cover of this character which is motivated by an electric motor or the like, the energizing circuits of which may readily be controlled, as by a key-operated switch. In combination with an arrangement of this character, an object of this invention is to provide a swimming pool structure that normally maintains its swimming pool covering position, and which cannot, short of physical destruction of substantial parts and/or provision of separate power mechanisms, be moved independently of the motor to pool-uncovering position. For this purpose, there is a strong spring-biasing arrangement which normally projects the cover into covering position. The motor itself serves merely to overcome the spring tension and to move the cover to retracted position. Thus, the spring structures resist opening movement of the cover by means other than the motor.

Another object of this invention is to provide apparatus of this character in which the operating mechanism is so controlled as to ensure against any accidents should there be any obstacle in the path of movement of the swimming pool mechanism.

This application is a continuation of my application Serial No. 733,338, filed on May 6, 1958, entitled Retractable Cover for Swimming Pools, now abandoned.

This invention possesses many other advantages, and

has other objects which may be made more clearly ap-A parent from a consideration of one embodiment of the invention. For this purpose, there is shown a form in the drawings accompanying and forming a part of the present specification. This form Will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a diagrammatic plan view of a swimming pool cover and its operating mechanism, and illustrated in pool-closing position; l

atent O FIG. 2 is a vertical sectional view diagrammatically illustrating the apparatus shown in FIG. 1;

FIG. 3 is a sectional view on an enlarged scale taken along a plane indicated by line 3--3 of FIG. 2;

FIG. 4 is a side view illustrating the mechanism for projecting the pool cover in a position intermediate retracted and projected position;

FIG. 5 is a sectional view taken along an offset plane indicated by line 5-5 of FIG. 4;

FIG. 6 is a view similar to FIG. 4 but illustrating the mechanism in projected position;

FIGS. 7, 8 and 9 are enlarged detail sectional views illustrating parts of the mechanism and taken, respectively, along planes indicated by lines 7 7, 8 8 and 9--9 of FIG. 4;

FIG. 10 is a plan View of the motor structure and its associated mechanism for operating the swimming pool cover;

FIG. 1l is a sectional View taken along a plane indicated by line lll-11 of FIG. 10, there being also diagrammatically illustrated in FIG. 1l the motor circuit;

FIG. 12 is a view of a portion of the mechanism illustrated in FIG. 11 in an alternate condition of operation; and

FIG. 13 is an enlarged pictorial view illustrating a portion of the cable.

In FIGS. 1 and 2, a swimming pool cover 10, made of strong, weather-resistant, pliant fabric, is projected in covering relationship over the entire area of a swimming pool 12. The ends 14 and 16 and the sides 18 and 20 of the swimming pool cover 10 project beyond the edges of the swimming pool 12 proper.

The cover 10 is supported at its sides 18 and 20 by companion retractable linkage structures 22, one of which is illustrated in detail in FIG. 4. These retractable mechanisms 22 move longitudinally along the opposite side edges or ledges of the pool 12, as shown in FIG. 1.

Referring now to FIG. 4, each mechanism 22 comprises a lazy-tong or pantograph-type linkage. A first set of links 24, 24a, 24b, 24C, 24d, in this instance in the form of tubular metal, are pivotally and serially connected t0- gether. These links extend in accordion or zig-zag relationship from a fixed anchor at one corner of the pool 12 and forwardly in a direction along the side of the pool. The anchor is provided by a clevis 28 fastened to a base 29 cemented or otherwise secured in position (see also FIG. 1). A pin 30, passing through the elements of the clevis 28 and through the end of the first link 24, mounts the link 24 for angular movement about a horizontal axis. The upper end of the first link 24 is pivotally joined to the second link 24a by the air of a pin 32 (see FIG. 7) that passes through aligned apertures at the upper ends of the links 24 and 24a. The lower end of the link 24a (see also FIG. 9) is pivoted to the succeeding link 24b by the aid of a shaft 34. Also mounted upon the shaft 34 is a wheel 36. Similar wheels are provided at the lower connection points of the links 24a-24b, 24a-24d, etc. to support the mechanism.

A second set of links 26, 26a, 265, 26C, etc. are also similarly pivotally connected together in series. The second set of links 26, 26a, etc. is located in staggered relationship to the first set, and so that the links of each set cross corresponding links of the other set. At the place of crossing, corresponding links of the respective sets are pivoted together as by pins 44, 46, 48, etc, (FIG. 8). A pantograph or lazy-tong linkage is thus provided. Accordingly, as the linkage elements are moved to the left (corresponding to the arrow 50 in FIG. 4), all of the links 24 and 26 assume substantially a vertical contracted position at that end of the pool l2 adjacent the anchor 28.

, When the links 24 and Ztmove` in the opposite direc-i 3 tion, the linkage expands, and each link assumes substantially a horizontal orientation as illustrated in FIG. 6, the end links extending to that end of the pool remote Ifrom the anchor 28.

The wheels 36 .are of 'such size that 'theiraxes :fallin a horizontal plane common tothe axis 'atthe anchor 28. The retracting mechanism accordingly moves horizontally orparallelto the edge of the pool. End tie bars 53 Vand intermediate tie bars54`have opposite ends secured' t'othe respective mechanisms'i'nA order to ensure that the respective .mechanisms line in parallellplanes. 'Diagonal braces 55, to be'described more'fully hereinafter, cooperate with the tie bars 5-4.and end bars '53`to Aensure that the parallel planes are'vertical. The tie bars 54 'are generally "of U-shaped conguration, 'the central connecting portions projectinginto the pool (FIG. 2) when the mechanisms are extended.

Eachtie bar 54 extends 'between corresponding upper pivotal connection points of the links of the respective mechanisms. Each tie bar V54 thus has adjacent each end a depending bar 56 (FIGS. 3 and 5) projecting between the ends of connected links. The bar 56 is apertured 'for reception of the corresponding pin 32. The central portions of the tie bars dip below the axis depressed by their mounting pins, and thus maintain the tie bars Vin Vvertical orientation.

The end bars have a slightly different coniguration in order to contact the ledges at the ends of the pool.

The end bars 53 are composite structures, as shown in FIGS. 4 and 7. A straight section 53a which extends across the pool, mounts a bar 56 at each end as do the tie bars 54. A U-shaped section 53h (FIG. 7) also extends across the pool. Its ends 53o are secured to the straight sect-ion 53a between the mounting bars 56 and the links 24 of the respective mechanisms. This ensures clearance with the iirst links 24 and 26 when the mechanism is projected (FIG. l).

There are ktwo braces 55 for each tie bar 53 (FIG. l). Each brace has ends connected respectively to the intermediate portion of the end bar element 53a and an adjacent link 24a, for example. Each brace 55 forms with thelink 24a and the end bar, a triangle (FIG. 4) that xes the orientation of the end bar 53 relative to the link 24a. Hence the end bars 53 change orientation as the mechanism is variously positioned. The partsare so proportioned that the end bars 53 assume a vertical orientation when the apparatus is projected. The braces 55, as stated previously, ensure vertical orientation of the mechanisms.

'The terminal portions of each tie bar 54 and the straight sections 53a of the end bars are downwardly returned to lie vertically along theV outer sides of the respective linkage mechanisms 22. These terminal portions together define, with the end bars themselves, elements of a boxlike frame for the cover 10.

The cover has box-like ilaps or flanges 10a (FIGS. 3 `and 7) secured to these elements by pins 58. The vertical portions of the tie bars 54 and the end bar sections 53a l'form bearing areas to prevent substantial direct strain upon the vpins 58. The cover 10 at the end 14 has cut-out corners, as at 11 (FIG. 7) for clearance of the end links 24 and 26 when the mechanism is projected. The Ycover 10 has an extended portion or flap 9 (FIG. 4) at the end of the device remote from the anchor end. This flap covers the end of the mechanism when it is retracted. Sides of the flap are folded inwardly before the mechanism is projected so that the length of the flap is less than the pool Width. Accordingly, the iiap simply dips into the water and out of the way as the device is projected. When the device is retracted, the sides are folded outwardly and detachably secured as by snap fasteners.

The central portions of the tie bars S4 lie sutiiciently beneath the `cover when projected to ensure against injury to any object or person falling at the central portion ofthe cover 10. When projected, the cover Vlies on the water surface (FIG. 3) whereby the water rather than the cover, 'absorbs possible impact.

The anchor brackets 28 (FIG. l) are located beyond the end of the pool a distance sufficient to allow the contracted links entirely to clear the end of the pool. For this reason, it is unnecessary to extend the cover to an area corresponding to the y'anchor brackets 28. Hence, one end bar S3 is at the end of the iirst link 24 of the iirst link set. No bar need be provided for the lirst link set. No bar need be provided for the tirst link 26 of the second link set of each mechanism. Hence, the first link 26 can be shortened.

The simple direct pivotal connection between the links of each link set is made possible Without limiting contraction of the linkage mechanism by alternate sidewise orienting the links. Thus, those links of the sets 24 and 26 which have corresponding angular orientation `lie in one plane at the inner side relative to the pool'12, and the other links lie in another plane at the outer side relative to the pool 12, the length of the pins 32, 34, and 48 corresponding to the spacing betweenthe planes. VA compact contracted relationship is thus made possible.

As many wheels 36 may be provided as necessary.A In the present instance, wheels are provided only at the lower, pivotally joined ends of the link set 24a-24h, 24e-24d, etc. Successive wheels 36 are on opposite sides of the links in order to avoid Vinterference upon contraction of the mechanisms.

In order to project the mechanisms 22, a number of spring structures are used. At vthe mid-level pivotal connections 44, 46, 48, etc. (see also FIG. S), there are coil torsion springs 66 mounted on the respective pins 44, 46, 43 between the connected links. Opposite ends, as illustrated in FIG. 8, of each torsion spring 66 engage opposed surfaces of the-respective links 24b and 26h, for example. One arm 67 of the spring has a curved end seated about the circular peripheral surface of the link 24h, and the other arm 68 is similarly seated on the link 2617. The torsion spring 66 `tends to rotate the .link 26h in a counterclockwise direction relative to the link 24b and vice versa. The net elect is to cause all of the links 24, 24a, 24b and 26, 26a, 26h, etc. to assume substantially a horizontal orientation as in FIG. 6 correspending to projection of the mechanisms.

The force provided by the springs 66 is supplemented by a series of similar springs 74 located at the lower pivotal connections between the link structures (FIG. 9). The spring 74, for example (FIG. 9), is located on the shaft 34 between the links which the shaft 34 .pivotally joins. rIhe springs 74 also tend to cause the links to assume their substantial horizontal orientation, as Villustrated in FIG. 6.

In order to retract the mechanisms 22 in unison and thereby to lift the cover 10 from closing position, a pair of cables or ilexible straps and 82 are provided (FIGS. l and ll). The cables extend from a common reel 84 (FIG. ll) located between the anchor brackets 28. As shown in FIG. 4, the cable or strap 80, for instance, extends between the links from the anchor base 29 and just above their lower pivoted connections (FIG. 9). 'Ille cable is secured at the end link 24e adjacent the lower end of the link.

Upon movement of the cable S0 to the left as viewed in FIG. 4, the linkage structure is contracted against the. force of the torsion springs. The end bars 53 and tie bars 54 are raised in unison, the springs eliminating slack in the mechanisms. The central connecting portions of the bars 54 raise from submerged position, as illustrated in FIG. 2. In the meantime, the axes at the upper ends of the links move toward each other and the distance between them diminishes uniformly. Slack is uniformly created in the cover 10 between adjacent tie bars. Normal fold lines at the coaxial upper ends of the tie bars 54 and end bars53 are produced, and the central portions of the tie bars enter between the folds. In the retracted position of the mechanisms 22, the cover l10 is clamped neatly between those links that would otherwise engage each other.

In order to avoid any toggle action that might interfere with the retracting movement, the parts are so proportioned that the links never quite reach a horizontal disposition. For this purpose, the cover has a length substantially equal to, but less than, the corresponding comlbined length of the links in any one of the sets of links 24 or 26.

For moving the cables Sti and 82 in unison, the winding reel 84 (FIGS. 10 and 1l) is operated by a motor 100. The winding reel 84 winds both the cables 8l) and 82 in unison, one cable S2 extending to the left of the reel 811; while the other extends to the right as viewed in FlG. l1. The cables 82 and Si) are guided by idler pulleys 8S respectively mounted at the anchor bases 29. The reel 3'4 has a collar or boss 9b aiiixed to a horizontal worm wheel shaft 92 journaled at opposite ends in brackets 94 and 96 (FIG. l0). The pulleys 83 impart an appropriate half-twist to the straps or cables Si) and 82. A worm wheel 97 mounted upon the shaft 92 is driven by a worm 9S aiiixed to the output shaft of the electric motor 100.

As the retracted movement of the cables Sti and 82 is begun, the radius at Which the cables Si) and 82 arelocated on the reel 84 is quite small. This produces a slow rate of initial movement of the cables S and 82 and, hence, a substantial mechanical advantage. This is appropriate because the rate of vertical rise of the mechanism relative to horizontal travel is at a maximum at the projected position illustrated in FIGS. 2 and 6. The

high rate of vertical rise relative to horizontal travel also means that at the extended position, it is virtually irnpossible to move the mechanism by hand. Thus to do so would mean lifting the entire cover at once and against the force of the springs 66 and 74. This is a crucial safety factor.

As the cables Wind up, the radius at the winding reel 84 increases and the speed accordingly increases with a decrease in mechanical advantage. This is appropriate because the rate of lifting decreases accordingly. Hence, by the use of the winding reel, it is possible to use the small-size motor 19t? that fullills the requirements of the mechanisms 22.

When the mechanisms 22 reach their retracted positions, the motor 191i is stopped. For this purpose, a circuit controller 102 in the energization circuit of the motor 111i) (FIG. 1l) is provided. The circuit controller 102 is mounted upon a bracket 111i adjacent the shaft bracket 92S and in the path of movement of the cable 82 between the reel S4 and the corresponding idler roller 80. A roller 112 mounted upon the bracket guides the cable S2 so that it normally passes just above the plunger 1116. Tape or other suitable abutment means 164 carried on one of the cables 32 engages an operating plunger 106 of the circuit controller 102 to interrupt the energization circuit of the motor 1119 when the mechanism is retracted. The springs in the mechanism 22 are ineffective to cause the mechanism to move to projected position when the motor 109 is stopped by virtue or" the fact that the worm 98 cannot be reversely driven through the worm wheel 97.

In order to move the traverse mechanisms 22 to projected positions, the energization of the motor 160 is reversed, the circuit controller 1192 being temporarily paralleled until such time as the abutment 104 clears the plunger 196. The springs then are operative to project the mechanisms.

It is important that the straps 80 and S2 move very nearly at identical rates. Otherwise, the paths of movement of the mechanisms 22 will curve, and one of them may pass over the edge ot' the pool. The single reel or pulley 84 ensures simultaneous and equal movement, and a track is not required.

Should either of the mechanisms 22 encounter any obstacle while the mechanism is being projected, the

cables and 82 will continue to move while the points of attachment of the cables to the mechanism will remain stationary. For safety purposes, the mechanism will automatically stop should slack occur in either of the cables. This is accomplished by the circuit controller 102 and by a companion controller 1103 for the respective cables. The controller 103 is mounted on a bracket 111 similar to the bracket 110, and a roller 113 similar to the roller 112 guides the cable 30 relative to the -controller 103.

In order to move the cable 82, for example, to engage the plunger 1%6 upon the existence of slack, an arm 115 is provided. 'Ille arm 115 is pivoted on the bracket 110 by a pin 11S. A roller 116 mounted on the arm is located opposite the circuit controller 102, and is urged to force the cable S2 to engage the plunger 196 by the aid of a weight 117 aixed to the arm at a place spaced from the axis provided by the pin 118. For moving the roller 116 away from the plunger 106 upon sutiicient tension in the cable, a post or roller 114 is provided. The post 114 provides a guide over which the cable 82 passes between the arm-mounted roller 116 and the bracket-mounted roller 112. The post is so located that the course of the cable changes direction as it passes the arm-mounted roller 116. Tension thus tends to straighten the cable 552, and hence to lift the roller 116 so that the cable 82 clears the plunger 106. The post 114 is so located that the tension tending to straighten the cable between post 114 and the bracket-mounted roller 112 does not detract from the desired movement of the arm 115 under conditions of suiiicient tension. Similar structures are provided for the cable 86.

When tension diminishes to a determined value, in either cable S0 or 82, one or both of the circuit controllers opens, as illustrated in FIG. l2.

Furthermore, the slack serves to deenergize the motor when the mechanisms reach their fully projected positions. In this instance, the end bars 53 or the tension in the cover 10 itself acts as an abutment, and the cables 80 and 82 continue to move slightly until the circuit controllers, or one of them operates.

The circuit controllers are serially connected between one line L1 (FIG. 1l) and one lead 120 or" the motor 166 which, in this example, is of the reversible capacitor controlled type. Two other leads 122 and 124 from the motor 100 connect across a capacitor 126. A doublethrow switch arm 123 connects another power line L2 to one side or the other of the capacitor 126 todetermine alternate directions of rotation of the motor litt).

To initiate movement of the motor 16), the switch arm 128 is reversed and a switch 131B which shunts the series-connected circuit controllers 192 and 1123 is momentarily closed. The motor then proceeds until either slack occurs or the abutment 1134i engages the plunger 106 as the case may be. Both the switch 131i and the switch arm 128 may be controlled by keys.

As shown in FIGS. l and 2, the end bar portion 53!) may pass beneath a small finger 134 to prevent the mechanism from being lifted at the end remote from the anchor brackets. The linger is mounted on a base plate 136 -cemented in position.

If desired, an enclosure 52 (FIG. 2) may be provided for the cover mechanism when contracted. That side of the enclosure 52 facing the pool provides an opening through which the mechanisms 22 and cover 10 pass.

The inventor claims:

1. In a retractable swimming pool cover: a pair of linked structures each defining an upright lazy tongs, each of the structures having a movable end element ground-engaging wheels carried by the structures for supporting the structures for traverse along the sides of a swimming pool; a foldable cover having sides secured to the respective structures; a series of resilient means between the links of the structures for extending the structures; and power means lfor contracting the structures in unison including a common reel, a pair of elements formed of flexible material wound in alternate layers on the reel and means respectively connecting the flexible elements to the said movable end elements of theV linked structures, said layers substantially increasing the effective diameter of the reel as the elements are wound thereon.

2. ln apparatus for covering a swimming pool or the like: a pair of lazy tongs type mechanisms, each comprising a first set of serially and pivotally connected links extending in accordion fashion, and a second set of serially and pivotally connected links extending in accordion fashion in staggered relationship to the links of the first set, so that the link sets cross each other; means pivotally joining the links of the respective sets at the area of crossing; means anchoring the end link of each mechanism at one end of the pool and orienting the links of the mechanisms for traverse along opposite edges of the pool; there being upper, intermediate, and lower axes of pivotal connection of the links of each of the mechanisms; a cover secured at opposite edges at the areas of the upper axes; spring means acting between pivotally connected links for urging the mechanisms to projected position; a pair of cables connected to links of the respective mechanisms remote from said end links for retracting the mechanisms in unison as the cables are moved in one direction and for permitting the mechanisms to be projected under the influence of said springs as the cables are payed out for movement in the opposite direction; a reversible motor drive connected to the cables for moving said cables in unison; means responsive to the existence of slack in either of the cables for interrupting operation of said motor drive; and means responsive to arrival of said mechanism to retracted position for interrupting operation of said motor drive.

3. The combination as set forth in claim 2, wherein circuit controllers for the motor drive are respectively positioned adjacent the normal path of the cables for providing the slack-responsive mechanism, and wherein one of said circuit controllers is operated by an abutment carried by the cable to interrupt said motor drive when said mechanisms arrive at the retracted position.

4. In apparatus for covering a swimming pool or the like: a pair of linkage mechanisms, each comprising a first set of serially and pivotally connected links extending in accordion fashion, and a second set of serially and pivotally connected links extending in accordion fashion in staggered relationship to the links of the first set, and so that the link sets cross each other; means pivotally joining the links of the respective sets at the area of crossing; an anchor having pivot means for one end link of each'mechanism, said anchors having provisions for attachment to concrete decking or the like for locating the said end links at one end of the pool and on opposite sides thereof, and for orienting the links of the mechanisms for parallel traverse in vertical planes along opposite sides of the pool; there being upper, intermediate, and lower axes of pivotal connection of the links of each of the mechanisms; wheels carried adjacent some of the lower axes and projecting at least partially beneath the linkage mechanisms at retracted, extended, and intermediate positions of the mechanisms for contacting the lateral surfaces along the pool and thereby supporting the respective mechanisms; the intermediate and upper axes having a vertical component of movement relative to the lower axes as the mechanisms traverse; the intermediate and upper axes moving vertically downwardly as the linkage mechanisms are extended, and moving vertically upwardly as the linkage mechanisms are retracted; and a flexible cover supported at opposite side edges between the respective mechanisms at places adjacent axes having a vertical component of movement for movement with said axes vertically downwardly as the linkage mechanisms are extended and vertically upwardly as the linkage mechanisms are retracted;

the cover having a length substantially equal to, but less than, the corresponding combined length of the links in any one of the sets of links so that the links of the respective mechanisms when fully extended lie substantially horizontally, whereby the cover may closely overlie the swimming pool, and whereby the cover has a higher rate of vertical rise relative to horizontal retracting movement at the extended position of the mechanisms than at the retracted position of the mechanisms.

5. The combination as set forth in claim 4 together with a plurality of separate springs for each mechanism, the springs being mounted at and acting on pivotally connected pairs of links to urge them toward unfolded extended position of the mechanisms, there being springs for pivotally connected link pairs from end to end of each mechanism whereby the springs act cumulatively to extend the mechanisms, and act uniformly to eliminate slack therein.

6. The combination as set forth in claim 4 together with a plurality of separate springs for each mechanism, the springs acting on pivotally connected pairs of links to urge toward unfolded extended position of the mechanisms, there being springs for pivotally connected link pairs from end to end of each mechanism whereby the springs act cumulatively to extend the mechanisms, and act uniformly to eliminate slack therein; and a pair of cables respectively for retracting the mechanisms, each cable extending from the anchor end of the mechanism to the opposite end thereof, the cable being attached to a link adjacent said opposite end; and power means connected to the cables for moving the cables in unison.

7. The combination as set forth in claim 4 together with a plurality of separate springs for each mechanism, the springs acting on pivotally connected pairs of links to urge toward unfolded extended position of the mechanisms, there being springs for pivotally connected link pairsV from end to end of each mechanism whereby the spring act cumulatively to extend the mechanisms, and act uniformly to eliminate slack therein; and a pair of cables respectively for retracting the mechanisms, each cable extending from that end of the mechanism adjacent the anchoring means to the opposite end thereof, the cable being attached to a link adjacent said opposite end; power means connected to the cables for moving the cables in unison; and bars extending between corresponding links of the mechanisms adjacent opposite ends thereof; and a finger beneath which the end bar, remote from anchoring means projects when the mechanisms are extended, and forming thereby a restraint against direct upward movement of said linkage mechanisms.

8. The combination as set forth in claim 4 together with tie bars extending between corresponding links of the respective mechanisms for supporting intermediate portions of the cover, said tie bars also being secured to the mechanisms adjacent axes thereof that have a vertical component of movement for vertical movement therewith, said tie bars determining a series of spaced folding axes for the cover as the traverse mechanisms are retracted.

9. The combination as set forth in claim 4 together with tie bars extending between corresponding links of the respective mechanisms for supporting intermediate portions of the cover, said tie bars also being secured to the mechanism adjacent axes thereof that have a vertical component of movement for vertical movement therewith, said tie bars determining a series of spaced folding axes for the cover as the traverse mechanisms are retracted, those tie bars extending across the pool when the mechanisms are projected having oitset portions projecting downwardly in the extended position of the mechanisms to project substantially beneath the surface of the pool whereby accidental impact with the tie bars by an object falling on the cover is substantially avoided, the lentral portions of the cover being unattached to the tie ars.

10. The combination as set forth in claim 8 together with braces between the end tie bars and the links of the respective mechanisms to maintain the links of the mechanisms against tilting from vertical planes.

References Cited in the tile of this patent UNITED STATES PATENTS 2,237,141 Gale Apr. 1, 1941 10 Campbell May 17, 1949 Kavanaugh Oct. 25, 1949 Karobonik et al. July 17, 1956 Lingard Apr. 16, 1957 FOREIGN PATENTS Great Britain Oct. 25, 1928 

1. IN A RETRACTABLE SWIMMING POOL COVER; A PAIR OF LINKED STRUCTURES EACH DEFINING AN UPRIGHT LAZY TONGS, EACH OF THE STRUCTURES HAVING A MOVABLE END ELEMENT GROUND-ENGAGING WHEELS CARRIED BY THE STRUCTURES FOR SUPPORTING THE STRUCTURES FOR TRANVERSE ALONG THE SIDES OF A SWIMMING POOL; A FOLDABLE COVER HAVING SIDES SECURED TO THE RESPECTIVE STRUCTURES; A SERIES OF RESILIENT MEANS BETWEEN THE LINKS OF THE STRUCTURES FOR EXTENDING THE STRUCTURES; AND POWER MEANS FOR CONTRACTING THE STRUC- 